The present invention relates to wet shaving systems of the blade type and more particularly to a shaving system having three or more movable blades positioned within a blade cartridge.
Shavers have long sought a smooth and close shave. In the pursuit to develop the ideal shaving implement, razor blade cartridges have been developed that include three blades. The triple blade configuration gives a closer shave than conventional dual blade configurations because three cutting edges are used rather than two cutting edges. However, the development of a triple blade cartridge raises the issue of proper orientation of the three blades to optimize razor performance.
A triple blade razor includes a minimum of five contact points that must be considered in order to optimize razor performance. Clearly, the cutting edge of each blade must be considered, but also a skin-contacting surface of a cap member and a skin-contacting surface of a guard member must be considered. Ideally, the shaving forces normal to the contacting surfaces are shared by all of the contacting surfaces, thereby distributing the shaving forces and preventing excessive scraping or nicking by one of the blade edges. The amount shaving forces on each edge is determined by the degree of blade exposure given to that blade. Consequently, the degree of "blade exposure" is crucial to optimizing razor performance.
The term "blade exposure" represents a geometrical relationship between the blades and other skin-engaging surfaces of the blade cartridge. The term "blade exposure" means the distance by which the blade edge projects forwardly of a shaving plane. The "shaving plane" is the plane tangent to skin-engaging surfaces, referred to as the guard member and the cap member, which are disposed on both sides of the blades so as to engage the shaving surface before and after engagement by the blade.
Triple blade razors have been developed that are concerned with proper blade exposure, for example, PCT International Publication Number WO 95/09071, published on Apr. 6, 1995, describes a razor blade unit including three blades mounted within a housing. The razor blade unit includes a guard, a cap, and three blades with parallel sharpened edges located between the guard and the cap. The leading blade has an exposure of less than or equal to zero, the trailing blade has an exposure of greater than or equal to zero, and the exposure of the middle blade is not less than the exposure of the leading blade and not greater than the exposure of the trailing blade. The preferred embodiment of the razor blade described in the WO 95/09071 publication has a progressive increase in blade exposure from the leading blade to the trailing blade, thereby reducing drag forces placed on the blade unit as it is moved over the skin of the shaver.
In the aforementioned patent, the first blade is restricted to an exposure of less than or equal to zero. The restriction of the first blade to a negative exposure or an exposure equal to zero significantly reduces the effectiveness of the first blade to give a close shave. The exposure of the first blade as set forth in the WO 95/09071 publication severely limits the ability of the edge of the first blade to contact the skin of the shaver and cut the hair close to the skin. Overall the invention described in the WO 95/09071 publication fails to achieve optimal blade geometry based on the lack of sufficient positive blade exposure.
In addition to the amount of blade exposure of the blades, a second factor in constructing a wet shaving system that provides a smooth and comfortable shave without having annoying cuts and abrasions is the "shaving angle" of the blades in response to shaving forces. The term "shaving angle" is defined as the acute angle between a plane tangent to the cutting edge of the blade and the shaving plane.
Consequently, a need exists for a triple blade cartridge incorporating optimal blade geometry wherein the shaving forces normal to the contacting surfaces is shared by all of the contacting surfaces to provide a close and comfortable shave. Such a blade cartridge should take into account such factors as proper blade exposure, and shaving angle of the blades in response to shaving forces.